Have the insides checked and cleaned and lubed etc. Clean the whole machine on the outside and treat the wood.
Leave the machine in its present condition as far as the paint goes and it will bring more money down the road if you ever sell it.
I have owned several old Mills machines and the ones I fully restored ( paint, wood etc) didn't bring as much as the ones I just cleaned up.
They only time I would ever do a paint job is if the machine had most of the original finish gone or real bad.
Walt